In the oldest systems, the gel which constitutes the medium is contained inside a glass vial, inside the interior of which the rod is broken after sample collecting.
The nearly total filling of the vial with the medium secures that the swab will be totally dipped inside the gel, even if during its transport, the vial undergoes impacts or overturning.
The poor practicalness of this system, and the contamination risk caused only those systems to be practically successful on the market, in which the sample collection rod is constrained to a plug, so that, after sample collection, the test tube which contains the medium can be closed by the cap provided on the swab rod.
In this way, the rod needs not be fractured after being dipped into the gel. However, the cap system is exposed to the following drawbacks.
During the transport, in particular when it is carried out by mail service, it is very likely that the test tubes suffer shocks and impacts, which may even be considerably strong, such as to cause the gel to get detached from the bottom and the walls of the test tube. The ultimate effect of such an occurrence is that the gel is frangmented into a plurality of particles, with it being consequently possible that the transport medium moves away from the region in which the nose of the sample bearing rod is.
Such a phenomenon of axial flow of the gel inside the test tube can cause the actual gel conditions to diverge, to a determining extent, from the conditions of survival of the microorganisms in the sample, thus causing the test to become unreliable.
One can hence realize how the devices of known type are not capable of securing a permanent and continuous contact between the sample collecting swab and the medium in gel form during the transport, and, therefore, a proper sample storage.
A further problem which conditions the reliability of sample storage derives from the undesired entraining of air bubbles, which is caused by the dipping of the rod which bears the sample into the "column" of gel medium contained inside the test tube.
The formation of these bubbles is very haphazard and depends on gel compactness, on the temperature the gel has at test tube use time, the gel age, the manual skill of the operator. The presence of air bubbles inside the gel, in particular when such bubbles are in the nearby of the sample, changes the aerobic/anaerobic condition of the system, thus potentially compromising the storage capability, in particular of anaerobic microorganisms.